Understanding subsurface geohydrology is of value in many circumstances. Examples include resource extraction operations such as mining, and oil and gas drilling; managing aquifers and surface water resources; and environmental investigation and cleanup.
One method for studying subsurface geohydrology involves placing a device for measuring temperature down a well boring along with an electrical conductor that may be heated. By analyzing the temperatures attained during heating, as well as the decay of such heating when the heating is halted, information about the geological structure and groundwater may be inferred. For example, if groundwater is moving horizontally near the well, it draws heat from the area, cooling that area of the well. This method may use a fiber optic temperature sensor system, known as a “distributed temperature sensor” or DTS. The DTS offers the advantage of precise temperature measurement over long distances with sub-meter spatial resolution and sub-minute temporal resolution.
While this method is sensitive to variations in structure and water movement near the well, the ability to detect and measure vertical water movement is poor. This is because the heating is uniform with vertical position, so there little difference with elevation to indicate vertical water movement. Additionally, it can be difficult to discriminate between horizontal and vertical water movements as reasons for cooling. The current invention combines the advantages and capabilities of existing systems with a novel heating arrangement that allows detection of vertical water movement within and near a well.